Incandescent lamp



Nov. 7, 1967 K. T. ZARINS 3,351,407

INCANDESCENT LAMP Filed Aug. 31, 1966 KARL T. ZARINS INVENTOR ATTORNEY United States Patent 3,351,407 INCANDESCENT LAMP Karl T. Zarins, Boxford', Mass., assignor to Sylvania Electric Products Inc, a corporation of Delaware Filed Aug. 31, 1966, Ser. No. 576,423 6 Claims. (Cl. 31625) ABSTRACT OF THE DISCLOSURE A method of manufacturing incandescent electric lamps having a tungsten filament in which the getter includes a small amount of iodine.

This invention relates to the manufacture of electrical lamps and more particularly to incandescent lamps of the vacuum type.

In the manufacture of most incandescent lamps of the vacuum type it is necessary that the tungsten filament in the finished lamp be physically stable and the atmosphere in the lamp be chemically pure. The attainment of these objectives is usually effected by flashing the filament and gettering the lamp. One of the operations in the manufacture of incandescent lamps is the application of a getter solution to the lamp filament or coil of tungsten wire. This is accomplished, for example, by dipping the coil in a phosphorous getter solution. After the lamp in process has been pumped down to about 10 microns, the lamp is flashed and the getter, by chemisorption and adsorption of residual gases, gets the lamp down to about 1 micron pressure.

Flashing of the lamp is effected by passing current through the filament for a short period of time at a voltage somewhat higher than the rated voltage of the lamp, i.e., the voltage at which the lamp, and particularly its filament, is designed to operate. This is done primarily to obtain a physical stabilization of the coil, although at the same time surface impurities on the tungsten coil are driven off and cleaned by the gettering action which occurs at the same time.

Tungsten wire, as it is received by the lamp manufacturer is characterized by a fibrous structure in which large numbers of long fibers of unequal length, some overlapping, are randomly arranged somewhat along the longitudinal axis of the wire. Tungsten wires in a fibrous state is not physically stable at operating temperatures. When shaped to form a lamp filament or coil and mounted it will tend to sag, the spacing between turns formed during coiling will not stay uniform and, upon the application of heat, the coil tends to twist and distort. To correct this condition the lamp is flashed.

Flashing of the lamp effects a recrystallization of the tungsten wire structure. Heating of the filament or coil during flashing causes a physical change in the fibrous structure. The fibers start to broaden and then form large interlocking grains, the boundaries of which are oriented somewhat parallel to the longitudinal axis of the wire. Recrystallization of the tungsten wire provides the desired physical stability of the coil; it will not sag or twist and the turns will retain their uniform spacing. However, when flashing is done at relatively high temperatures for a relatively long period of time, the coil can be adversely affected in that it tends to become quite brittle and very sensitive to mechanical shock, vibration, etc. Thus the lamp should be flashed at a temperature necessary to acquire the desired physical stability and yet not develop a significant brittleness. Ideally, the lower temperature required for flash over, the better the coil will be.

Thus one of the principal objects of this invention is to provide an incandescent lamp having a tungsten filament which is quite stable physically and yet has a high environmental resistance and a more uniform life. i

A further object of this invention is to provide an incandescent lamp having a tungsten filament which will flash over satisfactorily at or only slightly higher than the rated voltage of the particular lamp and filament type.

These and other objects, advantages and features are attained by introducing up to 3%, preferably about 0.5% iodine, into the getter solution normally employed in lamp manufacturing.

In the specific embodiment of the invention illustrated in the accompanying single figure of drawing, the lamp is a volt pilot light lamp. It comprises a substantially tubular glass lamp envelope 1 having a stem 3 disposed Within and hermetically sealed to one end thereof. The lamp is provided with a base-contact assembly comprising a wedge-like base 5 of suitable insulating material and a pair of metal clips 7. Each of the metal clips 7 is secured at one end thereof in the wedge-like base 5. The metal clips 7 are preferably shaped somewhat to the contour of the lamp envelope along which they extend. The segments of lead-in wires 9 and 11 which lie outside of the stem 3 are folded back along the sides of the lamp envelope 1 and are secured to the metal clips 7 by a suit able conducting cement. Thus the metal clips 7 define base electrical contacts for the lamp.

The mount structure of the lamp comprises a pair of lead-in Wires 9 and 11 sealed in and extending through the stem 3, a filament 15 and a plurality of filament support wires 17, 19 and 21. One end of each of the filament support wires is embedded in. the stem and the other end of each is looped around the filament 15. The filament 15 is secured at its ends to lead-in wires 9 and 11 and extends through and is supported by loops 17a, 19a and 21a of filament support wires 17, 19 and 21 respectively.

The manufacture of the lamp of the specific example just described is accomplished in the usual manner well known to those skilled in the art. The tungsten wire used for the filament is of small diameter, being about 0.24 milligram in 200 millimeters length. The wire is processed, shaped and mounted as a lamp filament in the usual manner. However, to the regular phosphorous dip getter there has been added 0.5 iodine solution.

Lamps are usually flashed at about 50% over the rated voltage. Thus, in the case of the 120 volt lamp of the specific example, one would normally flash the lamp at about volts. Usually it is necessary to get up this high in order to insure attainment of the necessary physical stability, i.e., non-sag, maintenance of uniform spacing between coils turns, etc. The desired recrystallization, obtained by flashing at voltages about 50% in excess of rated voltage, is accomplished by a certain amount of mechanical weakening in that the coils tend to get brittle and more sensitive to mechanical shock and vibration. However, I have found that when a 0.5 iodine solution is added to a conventional getter normally used in incandescent lamp manufacture, the flashing voltage may be reduced significantly. For example, the coils of lamps flashed at or only slightly over rated voltage readily attain the non-sag characteristic and retain their physical stability during life. This is a particularly distinct and definite advantage because of the corresponding gain in increased mechanical strength of the coil due to the lower flashing voltages, i.e., the coils are no longer subjected to the higher flashing voltages which contributed to the mechanical weakening of the coil.

While there has been shown and described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled inthe art that various changes and modifications may be made therein J Without departing from the invention as defined by the appended claims.

What I claim is:

1. The method of manufacturing an incandescent electric lamp having a tungsten filament, said method comprising applying a getter to said filament, said getter including a small amount of iodine.

2. The combination of claim 1 in which the getter includes about 0.5% iodine.

3. The combination of claim 1 in which the getter includes up to 3% iodine.

4. The combination of claim 1 and flashing said lamp by applying a voltage across said filament substantially less than 150% of the rated voltage of said tungsten filament.

5. The combination of claim 2 and flashing said lamp by applying a voltage across said filament substantially less than 150% of the rated voltage of said tungsten filament.

6. The combination of claim 3 and flashing said lamp by applying a voltage across said filament substantially less than 150% of the rated voltage of said tungsten filament.

References Cited UNITED STATES PATENTS 988,148 3/1911 Steinmetz 31625 1,944,825 1/1934 Millner 31625 3,132,278 5/1964 Collins 31625 RICHARD H. EANES, JR., Primary Examiner. 

1. THE METHOD OF MANUFACTURING AN INCANDESCENT ELECTRIC LAMP HAVING A TUNGSTEN FILAMENT, SAID METHOD COMPRISING APPLYING A GETTER TO SAID FILAMENT, SAID GETTER INCLUDING A SMALL AMOUNT OF IODINE. 